Fire officials believe seven children children were killed in a Wednesday morning fire in Philadelphia. The death toll is at 13.

Fire officials described it as a “tremendous loss of life” and a “sad, sad day” in Philadelphia.

Emergency crews responded to a fire inside a three-story rowhouse around 6:40 a.m. and discovered flames bursting from the second-floor windows.

During a press conference, officials noted there were four smoke detectors in the structure, none of which worked.

The investigation is on going. A cause of the fire has not been determined at this time.